To achieve highly efficient inventory and transport operations, it is beneficial to accurately track the movements of pallet loads, containers and other objects to be located and/or transferred as they are transported to and from various locations. In a worldwide inventory and transport business, a container, pallet of other object may, at any given time, be located at a manufacturer, in a warehouse, on a truck or ship, or may already be delivered to the final destination. In a worldwide system, the goods to be transported are picked up from one location, transported via truck, train and/or ship and then delivered. Due to the extremely high volume of containers, pallets or other objects, shipped everyday, it is difficult to keep track of these objects.
Additionally, once goods have been delivered to a particular destination, such as a warehouse, the goods may be located at various locations in the warehouse, such as storage locations, stocking locations, staging areas, and loading docks. In typical inventory and transport operations, the operator of a transport vehicle, such as a fork truck, reach truck, lift truck or pallet truck, receives a set of printed stocking or picking orders, typically generated by a computer, and executes the orders by visually identifying the loads and locations and transporting the loads to and from the locations specified on the orders. In such a system, especially in large-scale warehouses with a large number of locations and loads to handle, there are numerous opportunities for errors.
Some warehouse management operations use bar codes that are affixed to the loads or that mark specific locations. In a typical example of such a system, the operator uses a hand-held bar code scanner to read the bar code on the loads and, in some cases, on the stock locations. Although such a system is an improvement over purely visual processes, it may be difficult to completely implement, due partly to the need for direct line of sight, close proximity, and proper alignment between the scanner and barcodes. It also requires the operator to participate in the load-identification process. In some case, the operator may need to exit the transport vehicle to scan the barcodes manually, slowing down warehouse operations. Certain locations, for example high storage shelves and loading docks, often are particularly difficult places for using bar codes because of the need for close proximity between the codes and the reader. As a result, loads in those areas are often visually identified instead.
Radio Frequency Identification (RFID) transponders (tags) have been proposed as an alternative to bar codes. RFID tags are operated in conjunction with RFID base stations for a variety of inventory-control, security and other purposes. Typically an item having a tag associated with it, for example, a container with a tag placed inside it, is brought into a “read zone” established by the base station. The RFID base station transmits an interrogating RF signal that is modulated by a receiving tag. That is, the RFID base station generates a continuous wave electromagnetic disturbance at a carrier frequency and this disturbance is modulated to correspond to data that is to be communicated via the disturbance. The modulated disturbance, or signal, communicates the information at a rate, referred to as the data rate, that is lower than the carrier frequency. The receiving tag modulates the RF signal in order to impart to the signal information stored within the tag and then transmits the modulated, answering, RF signal to the base station.
In a typical conventional system, RFID tags containing information associated with the identities of inventory items to be tracked are attached to the inventory items. An RFID interrogator is used to detect the presence of an RFID tag and read the identification information from the tag. A typical RFID interrogator includes an RF transceiver for transmitting interrogation signals to and receiving response signals from RFID tags, one or more antennae connected to the transceiver, and associated decoders and encoders for reading and writing the encoded information in the received and transmitted RF signals, respectively. The interrogator may be a portable device, that may be brought near the tags to be read, or it may be a stationary device, that reads the tags as they are brought to the interrogator, as in the case of tagged library books being returned to a return station that is fitted with an interrogator. RFID tags may also be affixed near a location as a location marker. After detecting both a tag attached to an inventory item and a location marking tag, a processing unit associated with the interrogator may determine that the inventory item is positioned near the tagged location. While these conventional object tracking systems are capable of keeping a record of the inventory items and sometimes their locations, they are not effective for tracking and/or managing the movement of the inventory items.
There also exist warehouse inventory tracking systems that include fixed RFID interrogators at various locations to detect RFID-tagged items when they are positioned near the interrogator-equipped locations. For example, there are warehouses with RFID interrogators positioned at or near the loading dock gates. Such systems are capable of tracking the arrival of tagged items at the various locations, but are not capable of detecting errors remote to these locations. For example, if a fork truck picked up a wrong load because the truck was driven to a wrong pick-up location, the error would not be detected until the load had reached the gate. This delayed error detection negatively impacts the overall efficiency of warehouse operations. Additionally, outfitting each of the numerous loading dock gates with an interrogator is not cost effective.
RFID tags are categorized as either active or passive. Active RFID tags are powered by an internal battery and are typically read/write, i.e., tag data may be rewritten and/or modified. An active tag's memory size varies according to application requirements. The battery-supplied power of an active tag generally gives it a longer read range. The trade off is greater size, greater cost, and a limited operational life (that may yield a maximum of 10 years, depending upon operating temperatures and battery type).
Passive RFID tags operate without a separate external power source and obtain operating power generated from the reader. Passive tags are consequently much lighter than active tags, less expensive, and offer a virtually unlimited operational lifetime. Read-only tags are typically passive and are programmed with a unique set of data (usually 32 to 128 bits) that cannot be modified.
Read-only tags most often operate as a license plate into a database, in the same way as linear barcodes reference a database containing modifiable product-specific information. And, because they do not include a battery, “read-only” passive tags are typically much more “environmentally-friendly”.
Although field-powered passive tag RFID systems provide cost, reliability, and environmental benefits, there are obstacles to the efficient operation of field-powered passive tag RFID systems. In particular, it is often difficult to deliver sufficient power from a base station to a field-powered passive tag via an interrogating signal. The amount of power a base station may impart to a signal is limited by a number of factors, not the least of which is regulation by the Federal Communication Commission (FCC). An RFID tag may employ a resonant antenna in order to best utilize the signal power available to it. Unfortunately, a resonant antenna may require a good deal more area than is available to an RFID tag in many applications.
Additionally, one of the primary advantages of all types of RFID systems is the non-contact, non-line-of-sight nature of the technology. Tags may be read through a variety of substances such as snow, fog, ice, paint, crusted grime, and other visually and environmentally challenging conditions, where barcodes or other optically read technologies would be useless. RFID tags may also be read in challenging circumstances at remarkable speeds, in most cases responding in less than 100 milliseconds. However, even though line-of-sight is not required, in instances where the tag is blocked by other containers and/or wherein the non-line-of-sight is used to read the tag, the range of the tags is reduced, thereby reducing the effectiveness of the tags and leading to situations wherein a container or series of containers may become “lost” during transport.
Therefore, it would be beneficial to provide a system that provides increased accuracy to the process of object identification, movement and tracking throughout a transport, inventory, or other similar operation. There is a need for such a system that is adaptable for use with all of the wide variety of locations that are involved in inventory and transport operations, such as stocking locations, storage racks, floor lanes, warehouses, trucks, ships, and shipping docks.
The present invention is directed to alleviating one or more of the aforementioned problems, and meeting one or more of the above-identified needs.